Ground detector



June 22 1926. 1,589,699

L. F. HUNT GROUND DETECTOR Filed August 1925. 2 Sheets-Sheet 1 June 221926. 1,589,699

L. F. HUNT GROUND DETECTOR Filed August 1925 2 Sheets-Sheet 2 PatentedJune 22, 1926.

UNITED STATES PATENT OFFICE.

LLOYD I. HUNT, OF L08 ANGELEB, CALIFORNIA.

enounn nn'rnc'ron.

Application filed August :2, was. Serial No. scam.

This invention haste do with a ground detector useful for detectinggrounds in transmission or distributin lines, or the like, and it is anobject of t e invention to provide a device of this character which issimple, effective and reliable.

Grounds, for instance, in power transmission and distributing lines, areundesirable and wasteful and are often dangerous. It is, therefore,desirable to provide means for detecting grounds on such lines so thatthey can be investigated and remedied as quickan independent operatingcircuit; a relay ly as possible. Devices for this pur ose have beendevised and used, some of t em being more or less successful.

It is a general object of this invention to provide a practical and imroved device 0 the character above specifie The various objects andfeatures of my invention will be best and more fully understood from thefollowing detailed description of a typical preferred form and carryingout of the invention, throughout which description reference is had tothe accompanying drawings, in which Fi 1 is a face view of theinstrumentboar provided b this invention;

Fig. 2 is a si e elevation of the parts shown in Fig. 1, being a viewtaken as lndicated by the line 22 on Fig. 1;

Fi 3 is a rear view of the instrument board, being a view taken asindicated by the line 3-3 on Fig. 2; and

Fig. 4 is a diagram illustrating the invention.

The present invention is suitable for use in detecting grounds intransmission or distributing lines of various types. For the purpose offacilitating a clear understandmg of the invention I have disclosed itin a typical form and as applied to a threewire three-phase A-O powertransmission line, itbeing understood, of course, that the invention isnot to be considered limited to this specific form or application.

In the apparatus provided by my present invention there are threeprincipal potential transformers T, T, and T, connected in Y with thethree high tension power lines A, B,

and C; a voltmeter V, connected with the secondaries of the principaltransformers; resistance R in the connection between the transformersand voltmeter; a switch'S for \controlling a connection to the voltmeteraround the resistance R"; an alarm F, havin for controlling the alarmcircuit; and a control switch S for the relay G. y

All of the above named parts, except the transformers T, T and T may beadvantageously mounted on a single instrument board 10, so that theyform a unit that can be conveniently mounted in a suitable location. Inthe particular arrangement that I have illustrated in the drawings, thevoltmeter V, relay G, and control switches S and S are mounted on theface or front side of the instrument board 10, whilethe other parts aremounted on the back of the instrument board. The various connectionsbetween the parts on the instrument board are preferably arranged at therear of the board, as I have illustrated in Figs. 2 and 3 of thedrawings. i

The primary winding 11 of the transformer T has one side connected withthe line A by a connection 12, and the other side connected to groundthrough grounding connection 13. The primary winding 11 of thetransformer T has one side connected with the line B by a connection 12and the other side connected with ground through the connection 13. Thesecondary windings 14 14 and 14 of the transformers T, T and Trespectively, are connected in series by connections 15 and 16, one endof the series being connected with one terminal of the voltmeter B by aconnection 17, the other end of the series being connected with theother terminal of the voltmeter by a connection 18. The resistance R islocated in the connection 18. There is a connection 19 between theconnection 18 and the last mentioned terminal of the voltmeter aroundthe resistance R whereby the resistance R can be cut out. The switch Sis arranged in the connection 19 so that it controls the cutting out ofthe resistance R.

The signal F is preferably an audible signal, for instance, a bell. Inthe particular apparatus illustrated in the drawings, the bell F isadapted to be operated from an independent circuit, for instance, by a110 volt circuit, from a generator 20, or other suitable source ofenergy, through a suitable transformer 21. One side of the primarywinding 22 of the transformer 21 is connected with the enerator 20 by aconnection 23, while the ot er side is connected with the generatorthrough a connection 24. The relay G is arranged in the connection '24to control the energization of the transformer 21. The two sides ofthesecondary wind ing of the transformer 21 are connected w1th theterminalsof' the bell 26 by suitable- .nections 31 and 32, respectively,so that it is energized when there is flow through the CODIIBCtlOIlS' 17and 18 to the voltmeter V. The switch S for controllingthe relay G isarranged in one of the ,connections to the winding 30, for instance,connection 32, as I have illustrated in the diagram Flg. 4. The relay Gis such that when the winding is energized a predetermined amount itcloses the connection 24 so that the pnmary winding of the transformer21 is ener ized. v

n the particular apparatus illustrated in the drawings, I have providedextenslon lines 35 and 36 connected with the connections 27 and 28,respectively, for the purpose of operatin a second signal at a pointremoved from t e instrument boardlO, 1f so desired.

In a form of the invention where the transformers T,. T and T and thegener-.

ator 20 are separated from the parts carried by the instrument board,the connec. tions between the first mentioned parts and those carried bythe instrument board may be made through suitable binding posts 40provided on the instrument board, as I have clearly illustrated in Figs.1 and 3 of the drawings.

Under normal operating conditions the switch S is left open and theswitch S. is closed. Therefore, in practical construction the switcgswitch, adapte suitable push button, whereas, the switch S is preferablyan ordinary knife switch. When the high voltage lines A, B, and C areoperating without leakage to ground there is a balanced flow between thelines A, B, andC through the primary windings of the transformers T, Tand T The primaries of the transformers being connected in Y there is noflow through the secondary windings of the transformers or in thecircuit to the voltmeter V through the connections 17 and 18. Theprimaries being connected so that they are balanced the vector sum ofthe potentials of the secondaries is zero, so, therefore, there is noHow in the circuit to the voltmeter V. However, the moment a ound occurson any one of the main lines B, or C, the balance of the primaries ofthe transformers is disturbed causing a corresponding disturbance in thesec ondaries, and, therefore, flow in the circuit to the voltmeterthrough resistance R. The

' voltmeter V, of course indicates the extent S is preferably a button'to be actuated through aone of the main lines A, B, or C, the voltmeterV, due to the resistance R, will be only slightlyefi'ected. I preferablyconstruct the voltmeter so that it will indicate from zero to full roundwhen the resistance R is in and wifi indicate from zero to about tenpercent ground when the resistance is out out. When the ground is onlyslight and it is desired to obtain an accurate reading the switch S isclosed, cutting out the resistance R, giving a direct reading on thevoltmeter V.

, The relay G is such that it is actuated to close the connection 24when the ground is o f a certain predetermined amount, for instance, tenpercent. When the relay G is actuated the connection 24 is closedthereby causing energization of the transformer 21 so that the bell 26operates. In practice it is desirable to connect the primary winding ofthe transformer 21 in a circuit'of, say,

110 volts, and to roportion the transformer to suit such circuit and thebell 26.

In the apparatus I have provided anattendant can tell at any time, byexamining the voltmeter V, whether or not there is a ground on any ofthe main lines A, B, or C, and if there is an indication of a slightground, say, less then ten percent, he can obtain a ver accurate readingby actuating the switch g to out out the resistance B. At any time whenthe ground gets sufficient to operate the rela G the attendan'tsattention is called by t e operation of the alarm F. After theattendants attention has been called he can, of course, cut off thealarm by opening the switch S. Itis to be noted that the alarm isoperated directly from the circuit ofthe secondaries of the transformersthrough the relay and that it is not dependent upon operation of thevoltmeter or an other like device or instrument. The primaries of thetransformers are all permanently connected with the main lines so thatthere are no high voltage switches that require operation. Thetransformers being connected in the manner herein provided the voltmeteris not energized unless there is a ground on one of the main lines andvoltage variations in the main lines are balanced out so that they donot cause actuation of the voltmeter.

Having described only a typical preferred form of my invention I do notwish to limit myself of the specific details hereinabove set forth butwish to reserve to myself any changes or variations that may appear tothose skilled in the art or fall with- 1n the scope of the followingclaims.

Having described my invention, I claim:

1. In a ground detector for a three-wire system, a voltage indicator,and means connecting the voltage indicator with the three wires, saidmeans including three transformers having their primary windingsconnected in Y with the wires and their secondary windings connected inseries and with the voltage indicator.

2. In a ground detector for a three-wire system, a voltage indicator,and means connecting the voltage indicator with the three wires, saidmeans including three transformers each having one side of its primarywinding connected with one of the wires and the other side connectedwith ground, the secondary windings of the transformers being connectedin series and with the voltage indicator.

3. In a ground detector for a three-wire system, a voltage indicator,three transformers each having one side of its primary winding connectedwith a wire and the other side connected with ground the secondarywindings being connected in series, a circuit connectin the series ofsecondary windings with t e voltage indicator, and audible signal, anoperating circuit for the signal, a relay in the first mentioned circuitto control the operating circuit of the signal, and variable resistancein the first mentioned circuit.

In witness that claim the foregoing I have hereunto subscribed my namethis 9th day of LLOYD F. HUNT.

